Enucleation or envisceration of the eye is performed because of disease or trauma that make the removal of the eye necessary. Following such a procedure, the patient normally desires to have an artificial eye in order to restore a more normal appearance. In order to satisfactorily fit an artificial eye into the orbital socket, an orbital implant must be placed within the orbit to replace the volume within the orbit that was lost when the eye was removed. The use of an orbital implant and the subsequent fitting of the artificial eye confer more than a cosmetic benefit, however. They help maintain the normal structure of the eyelids and eyebrows; they aid in normal tear drainage; and, when used in children, they help stimulate normal growth of the orbital bones.
An early, and still typical, implant is a simple orbital implant in the form of a sphere or globe of plastic or other suitable inert material. When, after surgery, the socket (the area in the orbit that once held the eye) is healed, the socket is fitted with an artificial eye which lies on the tissues that have healed over the implant. Even though an artificial eye can be made today which has a very realistic appearance, the results from the patient's point of view are far from satisfactory. Without attachment of the eye muscles to the artificial eye, the artificial eye drifts within the socket and cannot be made to track with the normal eye. This lack of tracking is quite apparent and disconcerting to even a casual observer, creating a sense of self-consciousness on the part of the patient. As a result of this shortcoming of simple implants, efforts have been made to attach the eye muscles to the implant and then to attach the artificial eye to the implant. This procedure works quite satisfactorily in producing good tracking of the artificial eye. However, the success is short-lived because, in a brief period of time, the implant is extruded from the orbit. The reason for the extrusion of the implant is that the fixing of the artificial eye to the implant material exposes the implant to the outside environment. This permits bacteria to enter and the implant becomes chronically infected. This exposure is necessary, however, to produce the attachment between the implant and the artificial eye.
As previously noted, the typical implant is made of a non-natural material, at least as far as the patient is concerned. Materials that have been used include ivory spheres, gold globes, silk, catgut and a host of other materials. Acrylic plastics or silicones remain the materials of choice, however. To overcome the shortcomings of these materials, it has been proposed to use other more "natural" materials. Among these may be mentioned autoclaved human bone from cadavers, G. C. Sood et al., International Surgery, vol. 54, No. 1, p. 1 (1970), and antigenfree cancellous calf bone, so called "Kiel Bone", A.C.B. Molteno, et al., Brit. J. Opthal., vol. 57, p. 615 (1973) and A.C.B. Molteno, Trans: of the Ophthal. Soc. New Zealand, vol. 32, p. 36 (1980). Although varying degrees of success have been claimed for these materials, the method of choice remains, to this say, a simple implantation of an orbital implant which is typically made of acrylic, plastic or silicone, even though this deprives the implant of natural movement. No attempt is made to attach the implant to the artificial eye. However, extrusion of the implant is usually avoided and the implants is long-lasting.
As a result of the shortcomings of prior implants, there remains unfilled a long-felt need for an orbital implant which can be readily implanted in a manner which provides tracking of the artificial eye without the eventual extrusion of the implant, a problem which has characterized implants in the past.